Method for low-temperature cooling, liquefaction, and separation of gases



Jan. 25, MANN METHOD FOR LOW TEMPERATURE COOLING; LIQUEEACTIQN, AND SEEARATION OF GASES Filed March 5, 1924 Patented Jan. 25, 1 927.,

mnon iron row-mum My invention relates to a method for low.

. or known per se is used. In this case it IS I for the losses of cold of the 'ap aratus I compensation of the losses 0 cold 1s genmerely necessary to compensate, besides for the expenditure in energy caused by thereduction of entropy at the separation, ti rlily erall carried out by sending the gases under i them ow out expanded. .The heat content of the gases is less great under pressureso that in this -manner, when the gases are brought again by means of the counter current heat exchanger to the temperature of the'inflowing gases, permanently more energy is taken from the apparatus than sent into the same and this difference produces a cooling of the entire system until" the losses by absor tion of radiant heat have become equal to t e energy difference between them- 'flowing and the outflowing gases. "So S1111- ple is this kind of cooling, however 1t presents the grave inconvenience that the gas is compressed 'to' high pressure and that for this reason much valuable energy has to' be spent, Very high pressure (in practice generally 200 kg/cm) has to be applied especially at the startin of the apparatus when all the metaland nsulating masses of the same have to be cooled. Numerous ex eriments for improvement have already een made which however had all for their ob- 'ect to withdraw energv from the apparatus 1n any other less expensive manner. Expansion machines are used for this purpose which transmit the mechanical work to the outside but as such machines, in order to be effective, have to work at very low tem peratures they present considerable difliculties of service and have not been generally adopted. The cooling by means of ammonia machines comes also under this head'but the h pressure into the apparatus to let PATENT o FilcE.

snnrexnm, or 31mm, Gr mm.

COOLING, LI QUEILOI'IOPN', AND SEPARATION- or ems Application fled larch 3, 1884', Serial No. 098,588, and Germany lay as, 1922.

technical heatin effect of the same is very llmlted, the wor ing of the machine being further expansive and complicated.

, It m1g ht however be useful to load the gases which flow out of the apparatus with any'other form' of ener as heat andto let the same flow outof t e apparatus at this state, viz. with great velocity. The uestion is merely, how much energy is wit drawn from-the apparatus, that is to saywhich is the sum of the kinetic energy of the outflow.- mg gases plus their heat contents. From this point of view it serves no -pur ose to produce the high outflow velocity 'rectly at the outlet branch of the counter current ap aratus for instance in a nozzle) as in this case t e gases would escape at cold state, viz. with low heat contents. The velocity-must be produced already so far down in the apparatus that the outflowing ases have still the opportunity to re-heat t emselves in counter current up to approximately the temperature of the inflowinggases. The great velocity must therefore be maintained over long distances in opposition to the pipe friction. 'It is obvious that for this purpose a considerable decrease of pressure must be still at dis osal for the return.

travel of the gas and owmg to this condition the idea which is good and known per se has never been practically utilized for the hquefying of air. As the liquefying of air serves at the present times particularly for the purpose of the production of. oxygen it is rather difiicult to work under increased pressure a separation apparatus (column) which fulfills the modern requirements.

My invention differs from the above mentioned idea in that I abandon the high out;- flow velocity in the state of inertia and utilize the same merely for the starting of. the apparatus. .The following example is intended to explain theidea of the invention'i -'1lhe commonly used working method consists in starting at a pressure of 200 kg/cm and in expanding in the throttle valve to opproximately atmospheric ressuJ'eJ .Inthis case the refrigerating e ciency is 8.5 kcal/kg compressed air, supposed that the coolin water has atemperature of,17 CL If with the aid of this'refri rating dpflt? the apparatus had been cooled and a-fs duced for the rectification the pressure in the compressor was reduced, by opem the throttle valve further so that only the osses by adsorption of radiant heatwere covered,

approximately to 70 kg/cm so that the re the throttle valve to approximately atmospheric pressure and send the same at this state throu h the column and make the separated constltuentsflow out through the counter current apparatus. At the starting I do not however expand at the throttle valvc so far as stated but only to about kg/cm and I use this pressure to force the air in outward direction with a very great velocity. When the outflow velocity amounts to only about 250 m/sec. (in turbines and blowers much higher velocities occur) each kilogram of air draws along 7.5 kcal of kinetic energy so that the total refrigerating efliciency amounts in this case to 3.5+7.5:11.0 kcal/kg or to 30% more than acco'rdingto the commonly used methods.

If however the velocity in the end part of the counter current apparatus has to be greater at the starting than at the state of inertia either the quantity of gas which flows through must be greater or the free cross section must be made narrower.

I have therefore the possibility to increase the quantity of the air for the purpose of starting (instead as hitherto the pressure). It may therefore become necessary to 1ncrease the number of revolutions of the compressor or to work with several compressors for one apparatus, but in most cases it will be impossible to regulate the quantity, which flows through, in such a degree as it would be necessary but this kind of regulating might, under certain conditions be useful for the second manner of working according to the invention, which will be discussed later on. According to the invention the cross section for the outflowing gas is narrowed at the starting. The return conduit for the gases in the counter. current is composed of several tube-lengths of which only one or several are used for the starting, the other ones being shut oii. This methodpresents the inconvenience that the heat exchanging surface is smaller at the starting and in order to avoid this inconvenience I construct the counter current'apparatus in such a. manner that the return conduit for the gases is composed of several pipes which, at the state of inertia are connected in parallel and for the starting in series; or I interchange, for the purpose of the starting. the inflow pipe and the return pipe in the counter current apparatus in such a manner considerable increase of the metal mass and consequently a much longer starting time. In order to avoid this inconvenience I can disconnect the column from the main current and use the counter current apparatus merely air liquefying machine, the liquid produced being allowed to trickle off through the column siphon after it has expanded, the column being cooled atthe same time.

The advantages of my new method reside in the following :Less energy is consumed during the starting; according to the above cited example about 20% less than usual. This plays however, in comparison with the total consumption of energy of the plant, not an important part and what is much more important is that the cooling efficiency at the starting becomes greater and that the starting time is consequently shortened, accordin to the example given of about 30%. The main thing is however the absolute avoiding of the high starting pressure. Always the same end pressure of the compressor, for instance kg/cm is used. As all the different apparatus (separation apparatus, drying battery) pipe conduits, flanges, screws and the like must be calculated always for the highest ressure which could possibly occur, it is evi ent that a saving of expenses as well as a great simplification of the construction oi the compressor may be realized. To this is further added that the driving motor for the air compressor had to be dimensioned hitherto accord- 'ing to the efiiciency at the starting so that it was loaded at the state of inertia with only 80%. According to the improved method it runs always with equal efliciency so that it can be considerably smaller and is much cheaper and ada ted to work with its nominal efiiciency, VIZ. with the most favorable degree of efiiciency.

A form of construction of an apparatus adapted for carrying out the improved method is diagrammatically shown in Fig. 1 of the drawing.

A is the counter-currentheat exchanging apparatus, B the column.

During the state of inertia the air flows through the valve a with approximately 70 kg/cm and through the high pressure air conduit a and the evaporator coil f to the lid that thehigh pressure air flows through the valve f where it expands to about 1.3

kg/em' abs. and is delivered on the top of the column B. The nitrogen flows into the atmosphere through the valve 9, the counter current heat exchange A and the valve e. The oxygen flows out from the bottom part of the evaporator through the heat ex changer and through the valve d. The valves b, o, It and i are closed.

At the starting the air-flows at approxi mately 70 kg/cm through the valve 6 and the counter current heat exchanger A to be expanded in the valve h to approximately kg/cm, returns to the heat exchanger into the narrow high pressure tubes and flows out at great velocity through the valve 0. As soon as liquid has been produced it is expanded by the valve 11 to approximately 1 kg/cm abs. and it flows out through the column and through the oxygen tubes cl. The valves a, e, f and g are closed.

This invention relates further to a method for low temperature cooling, liquefaction and separation of gases in which only one of the constituents separated is expanded and flows out from the counter current ap paratus'with great velocity, the other constituent flowing out at a pressure above-atmospheric and with moderate velocity. This part of the invention is to be applied principally to the separation of mixtures containing hydrogen or helium, especially water gas. The hydrogen or the helium leaving the separation device slowly and under pressure, the more heavy constituent, especially the carbonic oxide, leaving the separation apparatus at great velocity and expanded, The advantage of this measure consists mainly in the fact that mixtures which contain more than 30% of hydrogen (and this is mostly the case) can be liquefied and separated while hitherto one had to proceed in a very complicated manner by re- .turning part of the carbonic oxide produced to the gas mixture to be separated.

A form of construction of an arrangement for carrying out this part of my invention is shown in. Fig. 2 of the drawing.

The gas mixture is admitted into the counter current apparatus A through the tube Z to be separated in the separation a paratus B. The carbonic oxide leaves t e counter current apparatus through the nar row tube at expanded and at great velocity, the helium or the hydrogen leaving the counter current apparatus through the wider tube m slowly and under pressure.

What I claim is: i

1. A method of low temperature cooling, liquefaction and separation of gases, which consists in causing the gases to flow through a countercurrent heat exchanging apparatus and to increase the rate ofspeed upon starting the process beyond the rate of speed of the flow maintained during the normal performance of the process.

2. A method of low temperature cooling, liquefaction and separation of gases, which consists in causing the gases to flow through a. counte'rcurrent heat exchanging apparatus, increasing upon starting of the process the rate of speed at which the gases leave the countercurrent heat exchan ing apparatus beyond that rate of speed which is maintained during the normal performance of the process, and causing upon starting the process at reduced temperature of the countercurrent heat exchan ing apparatus to flow in a larger volume t rough the apparatus than during the normal performance of the process. 1

In testimony whereof, I afiix my signature.

ARTHUR SELIGMANN. 

